Electronic isolator

ABSTRACT

The present invention is an electronic isolator that provides low input to output insertion loss, high output to input insertion loss, and substantial asymmetric isolation between a source circuit and a load circuit. The invention actively reduces noise and reflected power appearing on the isolator output. In numerous embodiments, the invention operates in circuit applications from dc through millimeter wave. Multistage electronic isolator embodiments provide increased isolation and greater noise reduction. In other embodiments, the electronic isolator also removes noise appearing on its input. In another embodiment, the invention is configured for high power applications. This embodiment includes circuitry for redirecting power away from the load into resistors or other dissipative elements. In another embodiment, the electronic isolator is configured to remove signal distortion produced by one or more power amplifiers in the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application No. 09/866,563, filedMay 25, 2001. The priority of this prior application is expresslyclaimed, and its disclosure is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of electronic isolators.

2. Background Art

Electronic circuits are often made up of a number of discrete “stages”where the output of a first stage is provided as input to a subsequentsecond stage. To maximize performance, it is sometimes desired toprovide isolation between the stages, so that the operation of the firststage is not affected by the operation of the second stage. Generally,this has been accomplished by employing an isolator between the circuitstages. However, currently available isolators suffer from a number ofdisadvantages.

Referring to FIG. 1, a multistage circuit is symbolically indicated. Thecircuit consists of a source stage 100 that provides output to a loadstage 120. The source and load stages are separated (and isolated) by anisolator 110. The isolator 110 minimizes unwanted interactions betweenthe source and load stage and protects circuitry of the source stagefrom damage due to power reflections from the load stage. Currentlyisolators are implemented by one of several methods, including magneticisolators and circulators, rat race circuitry, and resistive pads. Thesesolutions all have significant limitations in performance andapplicability.

Magnetic Isolators

The magnetic isolator is a common implementation of the isolatorfunction. Magnetic isolator devices use Faraday rotation todifferentiate between waves traveling in different directions. Amagnetic isolator generally consists of a magnetic material (typically aferrite) sandwiched between two poles of a permanent magnet. Theeffective operation of such a device requires that a significant portionof a wavelength be physically present in the device. This requirement inturn effectively determines the physical size of the magnetic isolator.(The size is also dependent on both the permitivity and permeability ofthe ferrite material as well as the strength of the permanent magnetthat is used to bias the ferrite material.)

The magnetic bias is used to create a non-reciprocal environment withinthe ferrite that induces a polarization change in a propagating wave.This polarization change is used to direct the wave along a particularpath, either to the output or to a dummy load. Since these devices makeuse of the wave characteristics of the signal, changing the frequencychanges the dependent phase characteristics, and the resulting isolationparameters of the isolator. The result is a relatively narrow banddevice (10%-20% being typical) that is relatively large and costly. As aresult, the use of magnetic isolators is typically restricted to certainapplications where the size can be accommodated, such as test equipmentand the interface between high power amplifiers and antennas being theprinciple applications.

Rat Race Circuit

The rat race circuit is a closed loop or circuit path. It relies on theconstructive and destructive interference of signals to produce lowinsertion loss and high isolation effects. If a transient signal isintroduced at a point along the closed path, it propagates in bothdirections. At some point(s) the two signals constructively interfereand an output port of the proper characteristic impedance can be locatedthere. The signals destructively interfere at the input port as theycontinue to propagate around the circuit or are reflected off the outputport. Similarly, it is possible to locate a point(s) where a signalinjected at the output port constructively interferes while at the sametime the same signal injected at the input destructively interferes.This point is the location of the third port in a circulatorconfiguration.

A disadvantage of the rat race approach is that as an interferencesystem, it is inherently narrow band. The second problem is that thepath length of the closed loop must be a significant portion of awavelength. Preferably, it will be several wavelengths long. Thus, evenat microwave frequencies, the path may be too long to be practical. Itis certainly much too long to be incorporated into an integrated circuitmuch below W-band.

Pads

Another approach has been the use of “pads” which are resistor networkshaving specified input and output characteristic resistances and aspecified attenuation of the input signal. Pads operate by attenuatingthe signals for both forward and reverse directions. This isolationreduces the amount of feedback to the source stage but requires thesource stage to provide a higher gain and output power to compensate forthe loss in the desired input to the load stage. For example, if it isdesired to have 10 dB of isolation between stages of an amplifier, thenthe pad would need to be a 10 dB attenuator and the previous stage wouldneed to have 10 times the gain and 10 times the output power. Thisadditional power requirement may be too expensive to achieve or mayunduly limit circuit performance.

Pads can be made asymmetric by having different input and outputresistances. However, these are typically used where a true impedancetransformation is desired. In most applications, the impedance levelsare the same and standardized to enable easy interface with commercialtest equipment. As a result, the use of isolation pads is usuallylimited to low power circuits and compensation for the loss is achievedby added gain stages, or added gain and power from the down streamcircuitry, an expensive and complicated solution.

SUMMARY OF THE INVENTION

The present invention is an active electronic circuit that is placedbetween the output of one electronic circuit (the source stage) and theinput of a second electronic circuit (the load stage) and provideshighly asymmetric attenuation of the electrical signals passing betweenthe two circuits. The asymmetric attenuation typically provides forrelatively low attenuation of the signal passing from the source to theload (usually a desired signal) and relatively high attenuation of thesignal(s) passing from the load to the source (usually undesiredsignals).

The present invention has the ability to simultaneously achieve highasymmetry between a low insertion loss and the high isolationattenuation, and to do so over a very much wider band of operation thanprior art configurations can achieve. The present invention is typicallysmaller, lighter and less expensive than prior art implementations, andthus can be incorporated into integrated circuits for low powerapplications.

In one or more embodiments, the present invention includes an electroniccircuit having general characteristics that approximate an ideal voltagecontrolled voltage source. This type of electronic circuit is non-idealand subsequently referred to as either a controlled voltage source or avoltage controlled voltage source.

In one embodiment, the present invention comprises a controlled voltagesource used in connection with a tee type resistor configuration toprovide isolation between source and load stages. The output of thecontrolled voltage source is set such that the tee leg of the circuithas a dynamic resistance that appears to be substantially infinite as toits impact on the source. In other embodiments, an active feedbackvoltage source is used which may or may not be gain adjusted, dependingon the application. In one of more embodiments of the present invention,the electronic isolator is implemented in a multistage configuration,with or without gain adjusted active feedback. In one or moreembodiments, the electronic isolator of the present invention is used infrequency band signal transmission applications. The invention may beused, for example, as part of a high power isolator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a multistage circuit with an isolatorbetween stages.

FIG. 2 is a block diagram of a multistage circuit with an electroniccircuit isolator of the present invention between stages.

FIG. 3 is a circuit diagram of a source stage used as an example in thepresent invention.

FIG. 4 is a circuit diagram of a load stage used as an example in thepresent invention.

FIG. 5 is a circuit diagram of one embodiment of the electronic isolatorof the present invention.

FIG. 6 is another embodiment of the electronic isolator of the presentinvention.

FIG. 7 is an embodiment of the electronic isolator of the presentinvention with active feedback.

FIG. 8A is an embodiment of the electronic isolator of the presentinvention with gain adjusted active feedback in which the tee legamplifier is within the feedback loop.

FIG. 8B is an embodiment of the electronic isolator of the presentinvention with gain adjusted active feedback in which the tee legamplifier is configured as a voltage source.

FIG. 9 is a circuit diagram of a multistage electronic isolator withcurrent sense.

FIG. 10 is a circuit diagram of a multistage electronic isolator withgain adjusted active feedback.

FIG. 11 is a circuit diagram of a multistage high power electronicisolator.

FIG. 12 is a circuit diagram of an electronic isolator implemented witha class A amplifier.

FIG. 13 is a circuit diagram of an electronic isolator implemented witha class A amplifier and emitter follower.

FIG. 14 is a circuit diagram of an implementation of the electronicisolator of the present invention to reduce power amplifier induceddistortion.

FIG. 15 is a circuit diagram of a radio frequency (RF) switch for a highpower electronic isolator implementation.

FIG. 16 is a circuit diagram of an implementation of the electronicisolator of the present invention using crossover networks fortransmission frequencies and frequency bands above the frequencyresponse band of tee leg operational amplifiers.

FIG. 17 is a circuit diagram of an implementation of the electronicisolator of the present invention for narrow band, forward signaltransmission with augmented, out-of-band isolation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an electronic isolator. In thefollowing description, numerous specific details are set forth toprovide a more thorough description of embodiments of the invention. Itis apparent, however, to one skilled in the art, that the invention maybe practiced without these specific details. In other instances, wellknown features have not been described in detail so as not to obscurethe invention.

The present invention enables electronic circuit designers to realizethe classic isolation function with an electronic circuit design asopposed to a non-linear physical process. This invention differentiatesthe source signal from the source signal plus noise reflected from theload. This noise may include out-of-phase source signal or harmonicdistortion induced by a nonlinear device such as a diode or transistor.This invention uses no magnets or magnetic materials. It is notwavelength sensitive and as such is wideband with no significantfrequency sensitivity.

Since it does not use large magnetic components, one or more of thesedevices can be integrated into a single integrated circuit. Thisintegration capability results in a true, low insertion loss isolator.

In the various embodiments of this invention, the circuits are typicallyshown as purely resistive networks. This is done to provide the clearestdescription of the operation of the electronic isolator. This does notimply that reactive elements and networks cannot be included. Bothseries and parallel tuned circuits can be included in any leg of theisolator to shape performance and response. The circuit designer needonly understand the nature of the response shaping being undertaken andthe effects of the reactive networks on system performance parameterssuch as frequency response, phase shift, and attenuation.

In many of the Embodiments shown, the active devices are shown asbipolar junction transistors. Any of the embodiments can also beimplemented with Field Effect Transistors (FETs), vacuum tubes, tunneldiodes, optical isolators, magnetic regulators or other gain capabledevices.

FIG. 2 illustrates a block diagram of the invention. The invention,being an electronic circuit design instead of a physical process, isreferred to as an electronic circuit isolator or electronic isolator inthis description. The electronic isolator 210 is shown between a sourcestage 200 and load stage 220.

Source Block

FIG. 3 illustrates an example 300 of source stage that may be used withthe present invention. Source stage 300 comprises voltage source V301coupled to ground at its negative terminal and to resistor R301 at itspositive terminal. Resistor R301 is coupled to node N301 oppositevoltage source V301. V301 represents the signal source (e.g., from anamplifier stage). R301 represents the source resistance. In practice,R301 may comprise any number of circuit resistance topographies. Thissource structure is typical for the other embodiments.

Load Block

FIG. 4 illustrates an example 400 of a load stage in the presentinvention. Load stage 400 comprises voltage source V401 coupled toground at its negative terminal and to impedance Z401 at its positiveterminal. Load impedance Z402 is coupled to impedance Z401 at Node N401.At its opposite terminal, Z402 is coupled to ground. Voltage source V401represents the source of noise being injected into the system throughits source impedance Z401. The noise can consist of a variety ofcomponent parts. These include an out of phase portion of the inputsignal power that reflected off the load, feedback of electronic noisegenerated or picked up by down stream circuitry, radiated and couplednoise from nearby circuitry or lines injected into this circuit or itsoutput cable. It also can include distortion, as well as thermal, shot,or other internally generated noise. There will typically be more thanone noise source each with its own characteristic source impedance andequivalent injection point. Only one is shown to simplify the figure.This noise structure is typical for the other embodiments.

Electronic Isolator Circuit

FIG. 5 illustrates an embodiment of the present invention. T-Network 500is coupled to source block at node N301. T-Network 500 is coupled toload block at node N401. Isolator input resistor R501 is coupled tosource block at node N301 and to isolator output resistor R503 at nodeN501. Resistor R503 is coupled to load block at node N401. Tee resistorR502 is coupled to resistor R501 and resistor R503 at node N501. Voltagesource V501 is coupled to resistor R502 at its positive terminal and toground at its negative terminal.

Tee-resistor R502, in conjunction with the gain and source resistance ofvoltage source V501, determine the range and amount of current injectedor sunk to cancel the noise present. Voltage source V501 should beselected to be as close to an ideal voltage source as is practical andappropriate for a specific application. This helps to localize the powerdissipation in the resistors rather than the controlled source.

In this configuration, with noise voltage V401 equal to zero, thecircuit is configured so that there is no current flowing through R502.This is accomplished by selecting V501 with a gain equal to thatproduced by voltage source V301 at node N501. Since there is no currentflowing in the tee leg, the resistance of the tee leg appears infinite.For example, if V301 is 1 Volt (V), source resistance R301 and loadimpedance Z402 are nominally 50 Ohms, R501 and R502 are 1 ohm, and R503is 9 ohms, the current through R501 will be 9.091 milliamperes andvoltage source V501 should be selected to be 0.983333 V. Insertion lossfor the electronic isolator in this example is approximately 0.79 dB.

Assuming the addition of noise source V401 to the circuit with a sourcevoltage of 10V and Z401 equal to 50 ohms, the nominal noise voltageappearing at Node N301 is 0.137 V and the achieved isolation isapproximately 12.9 dB.

Electronic Isolator Circuit with Voltage Controlled Voltage Source

FIG. 6 illustrates an embodiment of the present invention in whichisolator voltage V601 is a controlled voltage source. T-Network 600 iscoupled to source block at node N301. T-Network 600 is coupled to loadblock at node N401. Isolator input resistor R501 is coupled to sourceblock at node N301 and to isolator output resistor R503 at node N501.Resistor R503 is coupled to load block at node N401. Tee-Resistor R502is coupled to resistor R501 and resistor R503 at node N501. Voltagesource V601 is coupled to resistor R502 at its positive terminal and toground at its negative terminal. Voltage controller V602 is coupled tosource block at node N301 at its positive terminal and coupled to groundat its negative terminal.

T-Network 600 essentially functions like T-Network 500, although thereplacement of voltage source V501 with controlled voltage source V601means that the isolator voltage source does not need to be replaced indivergent circuit conditions.

Electronic Isolator Circuit with Active Feedback

FIG. 7 illustrates an alternate embodiment of the present invention inwhich the T-Topography of FIGS. 5 and 6 is replaced by an operationalamplifier in a negative feedback configuration. Electronic Isolator 700is coupled to source block at node N301. Isolator 700 is coupled to loadblock at node N401. Resistor R501 is coupled to the source block at nodeN301 and to resistor R503 at node N501. Resistor R503 is coupled to loadblock at node N401. Operational amplifier A701 is connected at itspositive terminal to the source block at node N301. The negativeterminal of A701 is coupled to node N501. The output of A701 is coupledto node N501. Resistor R502 is coupled to resistors R501 and R503 atnode N501.

As in the T-Topography circuit configuration, V301 represents the signalsource (such as a previous amplifier stage) with a source resistanceR301. Noise source V401 represents the source of noise being injectedinto the system through its source impedance Z401. Impedance Z402represents the input impedance of the next circuit. Resistors R501, R502and R503 are the tee resistors and A701 is an operational amplifierperforming the role of a high gain voltage source.

There may be a tendency in this circuit for amplifier A701 to force thecurrent in R501 to zero and supply the load current itself. If R502 doesnot match the load impedance Z402, power transmission will be reducedand dissipation in the operational amplifier increased. This problem isalleviated in another embodiment by providing a gain adjustment for thecircuit that produces an accommodation for the voltage drop across R501.

Electronic Isolator Circuit with Gain Adjusted Active Feedback

FIG. 8A illustrates an embodiment of the present invention in which thecircuit of FIG. 7 is implemented with a gain adjustment network.Electronic isolator 800 is coupled to source block at node N301.Isolator 800 is coupled to load block at node N401. Resistor R501 iscoupled to the source block at node N301 and to resistor R503 at nodeN501. Resistor R503 is coupled to load block at node N401. Resistor R801is coupled to node N301. Resistor R802 is coupled in series to resistorR801 at node N801 and to ground. Operational amplifier A701 is connectedat its positive terminal to node N801. The negative terminal of A701 iscoupled to node N501. The output of A701 is coupled to resistor R502.Resistor R502 is coupled to Resistors R501 and R503 at node N501.

In one embodiment, the isolator circuit is implemented with a dividernetwork (R801 and R802) that attenuates the input signal from voltagesource V301 to provide the reference signal for the operationalamplifier. In this embodiment, the adjustment provided by the dividernetwork is the nominal value of the voltage drop across resistor R501.Moreover, the operational amplifier does not attempt to force theTee-Junction to match the input voltage, as may occur in the embodimentillustrated in FIG. 7. In another embodiment, the circuit activelycalculates and tracks the R501 loss in or near real time if loadimpedance Z402 varies significantly.

Repeating the example shown with FIG. 6 (V301=1 V, R501=1 Ohm and R503=9Ohm), assuming that the operational amplifier output current has beenmade zero by the feedback mechanism, and selecting R801=1000 Ohm, R802should be 59,000 Ohm. Neglecting the current through the dividernetwork, the current through R501 is again 9.091 milliamperes.

With respect to the injection of a similar noise source (V401=10 V andZ401=50 Ohms) into the circuit, the following assumptions are made forthe purpose of example only. First, the noise source is the largest withwhich the electronic isolator must cope. Second, the maximum voltageswing for Amplifier A701 is ±12 Volts.

At an instantaneous noise voltage of 10 Volts, the output of AmplifierA701 is at its negative maximum of −12 volts. Solving the equations forthe injected noise to be 0 at Node 501 implies the value of R502 shouldbe approximately 82 Ohms. In this example, the noise appearing on theinput is 0 and the isolation is infinite. The achievable performance issignificantly improved compared to the open loop versions of theelectronic isolator.

Due to the gain of the amplifier A701, the value of R503 is much largerthan the 1 ohm Tee Resistor in the FIG. 5 example. The resistance ofR503 can vary as long as amplifier A701 is not allowed to rail or exceedits current source/sink capability during normal operation. In practice,there are several reasons for considering this calculated value of R503to be an upper limit and selecting a value that is smaller. First, anynoise sources present are not likely to be well characterized with knownmaximum amplitudes. Second, the presence of reactive parasitic elementsin the system or possible antenna induced, high VSWR conditions canresult in larger than normal peak amplitude voltages being encountered.In both cases, it is desirable to provide the operational amplifier withas much headroom as practical to attempt to correct the condition.Third, a larger than necessary output swing on amplifier A701 can induceadditional time delay and the associated potential distortion (see timedelay discussion in the multistage versions below), or can require theuse of a more costly, higher slew rate operational amplifier. Fourth,larger resistors generate more thermal noise that could degrade theperformance of very low nose systems.

An alternate embodiment of the gain adjustment network is shown in FIG.8B. In this embodiment, the negative feedback is taken directly from theoperational feedback output with a significantly reduced value for TeeResistor R502. Electronic isolator 805 is coupled to source block atnode N301. Isolator 805 is coupled to load block at node N401. As in theprevious embodiment, resistor R501 is coupled to the source block atnode N301 and to resistor R503 at node N501. Resistor R503 is coupled toload block at node N401. Resistor R801 is coupled to node N301. ResistorR802 is coupled in series to resistor R801 at node N801 and to ground.Operational amplifier A701 is connected at its positive terminal to nodeN801. The output of A701 is coupled to resistor R502 at Node N802. Theoutput of amplifier A701 is fed back to the negative terminal at NodeN802. Resistor R502 is coupled to Resistors R501 and R503 at node N501.

In one embodiment, the isolator circuit is implemented with a dividernetwork (R801 and R802) that attenuates the input signal from voltagesource V301 to provide the reference signal for the operationalamplifier. In this embodiment, the operational amplifier functions as aclassic voltage source. In still another embodiment, Tee Resistor R502is replaced by two resistors and feedback to Amplifier A701 is takendirectly from the midpoint.

Multistage Electronic Isolator Circuit with Current Sense

FIG. 9 illustrates an alternate embodiment of the present invention,which is a multistage circuit with current sense. Electronic isolator900 is coupled to source block at node N301. Isolator 900 is coupled toload block at node N401. Input resistor R901 is coupled to source blockat node N301. Output resistor R904 is coupled to load block at nodeN401. Resistors R902 and R903 simultaneously function as both input andoutput resistors for Tee stages in the isolator circuit. Resistor R902is coupled in series to input resistor R901 at node N901. Resistor R903is coupled in series to output resistor R904 at node N903 and in seriesto resistor R902 at node N902.

Resistors R910, R911 and R912 are the Tee Resistors for controlledvoltages sources V901, V902, and V903, respectively. Accordingly,resistor R910 is coupled to resistors R901 and R902 at node N901.Controlled voltage source V901 couples resistor R910 at its positiveterminal to current sense resistor R913 at its negative terminal.Resistor R913 couples V901 to ground. Resistor R911 is coupled toresistors R902 and R903 at node N902. Controlled voltage source V902couples resistor R911 at its positive terminal to ground at its negativeterminal. Resistor R912 is coupled to resistors R903 and R904 at nodeN903. Controlled voltage source V903 couples resistor R912 at itspositive terminal to ground at its negative terminal. In one embodiment,resistors R905, R906, R907 and R908 form a low power, divider networkwhich sets the input voltages of controlled voltage sources V901, V902and V903 to the values at the respective Tee Nodes. Accordingly, theresistances of these components are typically proportional to thecorresponding series resistor in the primary power path. Thus, resistorR905 couples source block at node N301 to the controller for V901. Theresistance of R905 is proportional to the resistance of R901. ResistorR906 is next in series and couples the controller for V901 to thecontroller for V902. The resistance of R906 is proportional to theresistance of R902. Resistor R907 is next in series and couples thecontroller for V902 to the controller for V903. The resistance of R907is proportional to the resistance of R903. Resistors R908 and R909complete the divider network and couple the network to ground.

As in previous figures, V301 represents the signal source (such as aprevious amplifier stage) with its source resistance R301. V401represents the source of noise being injected into the system throughits source impedance Z401. Z402 represents the input impedance of thenext circuit, and is typically complex. Since Z402 is typically unknown,it will sometimes be necessary to adjust the value of R909 to achieve anoptimal balance between the two resistor strings. In one embodiment, thecurrent in sense resistor R913 is measured and the value of R909 isadjusted to reduce the R913 signal current to zero.

Multistage Electronic Isolator Circuit with Gain Adjusted ActiveFeedback

FIG. 10 illustrates an embodiment of the present invention which is athree stage isolator circuit with the first two stages implemented withthe operational amplifier embodiment shown in FIG. 8A. The third stageis shown implemented with an amplifier capable of dissipating themaximum forward power driving the isolator input. It is important thatthe high power dissipation is concentrated in R1006 and V1001 or thepreceding stage(s) will also need to be power amplifiers. Thisembodiment with power dissipation concentrated in the output stage isused at low and medium power levels. In another embodiment, the laststage is an operational amplifier capable of dissipating the fullincident power. An alternative embodiment incorporates an operationalamplifier driving another amplifier circuit.

Accordingly, electronic isolator 1000 is coupled to source block at nodeN301. Isolator 1000 is coupled to load block at node N401. In the firststage, resistor R1001 is coupled to the source block at node N301 and toresistor R1003 at node N1001. Resistor R1008 is coupled to node N301.Resistor R1009 is coupled in series to resistor R1008 at node N1004 andto ground. Operational amplifier A1001 is connected at its positiveterminal to node N1004. The negative terminal of A1001 is coupled tonode N1001. The output of A1001 is coupled to resistor R1002. ResistorR1002 is coupled to resistors R1001, R1003 and R1010 at node N1001.

In the second stage, resistor R1003 is coupled to resistor R1001 at nodeN1001 and to resistor R1005 at node N1002. Resistor R1010 is coupled tonode N1001. Resistor R1011 is coupled in series to resistor R1010 atnode N1005 and to ground. Operational amplifier A1002 is connected atits positive terminal to node N1005. The negative terminal of A1002 iscoupled to node N1002. The output of A1002 is coupled to resistor R1004.Resistor R1004 is coupled to resistors R1003 and R1005 at node N1002.

The third stage is a T-Topology configuration. Accordingly, outputresistor R1007 couples load block at node N401 to input resistor R1005.Tee Resistor R1006 couples controlled voltage source V1001 at itspositive terminal to resistors R1005 and R1007 at node N1003. Thenegative terminal of controlled voltage source V1001 grounds thecircuit. In one embodiment, the controller for V1001 is coupled to loadblock at node N301 and to ground.

The multistage configuration introduces time delays into the operationof the electronic isolator. At low frequencies (up to at least severaltens to hundreds of megahertz), the combined time delay and slew ratecapability of the available operational amplifiers means the isolationprocess does not introduce significant distortion on the incidentwaveform. In one or more embodiments in which the electronic isolatorprocesses higher frequencies, it is necessary to match time delays inthe circuitry. The embodiment shown in FIG. 10 passes a sample of theinput signal directly to the third stage in a form of feed forward,which is used to minimize the distortion effects introduced by circuittime delay. In alternate embodiments, the feed forward is applied to oneor more interim stages. In still other embodiments, the feed forwardincludes circuitry to provide an adjustable time delay for more precisematching of the incident power form.

Multistage High Power Electronic Isolator

One of the functions of an isolator is protection of the electroniccircuitry driving its input port from variations in the load circuitryon its output port, particularly in high power applications. Theseconditions typically include both open and shorted outputs.

The protection function provided in the prior art by magnetic isolatorsis provided in one or more embodiments of the present invention.Internal dissipation of the reflected power requires the source in thelast stage to handle nearly the full incident power for at least a shortperiod of time. In general, this is the equivalent of adding a secondhigh power amplifier to the system, and represents a significant sizeand cost effect on the system. This is mitigated by making the isolatoroutput stage amplifier have pulse power capability equivalent to themaximum output power of the source. Dumping the power into a dummy loadis an alternative that requires both fault sensing and power switchingcircuitry that requires time to operate. A high pulse power isolatoroutput stage amplifier embodiment mitigates the cost of an isolator ascompared to an embodiment that must handle the same power on acontinuous basis.

One advantage of switching the power into a dummy load is that theprotective function is contained within the electronic isolator and doesnot require interstage communication of control signals. If a protectionsystem is configured wherein control signals are generated to turn-off,reduce, or redirect the electrical input power to the isolator, thecontrol signals typically require a time delay capability to accommodatenormal functions such as turn-on or short term, self correctinganomalies.

FIG. 11 illustrates an embodiment of the electronic isolator inaccordance with the present invention in which an RF switch isincorporated into the circuit of FIG. 10 to “open” the circuit pathbetween the isolator source and load circuitry. A diode switch is thepreferred method due to its relatively high speed. (An example of such aswitch including potential features and characteristics is shown in FIG.15.)

Accordingly, electronic isolator 1100 is coupled to source block at nodeN301. Isolator 1100 is coupled to load block at node N401. In theembodiment illustrated in FIG. 11, resistor R1001 is coupled to thesource block at node N301 and to resistor R1003 at node N1001. ResistorR1008 is coupled to node N301. Resistor R1009 is coupled in series toresistor R1008 at node N1004 and to ground. Operational amplifier A1001is connected at its positive terminal to node N1004. The negativeterminal of A1001 is coupled to node N1001. The output of A1001 iscoupled to resistor R1002. Resistor R1002 is coupled to resistors R1001,R1003 and R1010 at node N1001. Resistor R1003 couples the second stageto the first stage at node N1001. Resistor R1003 is coupled to resistorR1005 and R1004 at node N1002. Resistor R1011 is coupled in series toresistor R1010 at node N1005 and to ground. Operational amplifier A1002is connected at its positive terminal to node N1005. The negativeterminal of A1002 is coupled to node N1002. The output of A1002 iscoupled to resistor R1004.

The third stage is a T-Topology configuration. RF switch 1500 isincorporated between output resistor R1007 and the T-Branch.Accordingly, output resistor R1007 couples the load block at node N401to RF switch 1500. Tee Resistor R1006 couples controlled voltage sourceV1001 at its positive terminal to resistor R1005 and RF switch 1500 atNode N1101. The negative terminal of controlled voltage source V1001grounds the circuit. In one embodiment, the controller for V1001 iscoupled to the source block at node N301 and to ground.

Electronic Isolator Implemented With Class A Amplifier

An embodiment of the present invention in which the isolator isimplemented with a class A amplifier is illustrated in FIG. 12.Electronic isolator 1200 is coupled to source block at node N301.Isolator 1200 is coupled to load block at node N401. N-Type transistorQ1201 and resistors R1201, R1202, R1203 and R1204 comprise Class Aamplifier 1205. Positive voltage bias V1201 couples amplifier 1205 toground at node N1201. Negative voltage bias V1202 couples amplifier 1205to ground at node N1204. Resistors R1201 and R1202 are coupled to thepositive voltage bias V1201 at node N1201. Resistor R1201 is coupled tothe base of transistor Q1201 at node N1202. Resistor R1202 is coupled tothe collector of transistor Q1201 at node N1203. Resistors R1203 andR1204 are coupled to negative bias V1202 at node N1204. Resistor R1203is coupled to the base of transistor Q1201 at node N1202. Resistor R1204is coupled to the emitter of transistor Q1201 at Node N1205.

DC blocking capacitor C1201 is used to AC couple the reference signalinto amplifier 1205. Accordingly, C1201 couples source block at nodeN301 to the emitter of Transistor Q1201 at Node N1205. DC blockingcapacitor C1202 is used to AC couple the feedback signal into theamplifier. Accordingly, C1202 couples the base of transistor Q1201 atnode N1202 to node N1206. Isolator input resistor R1205 couples sourceblock at node N301 to capacitor C1202 at node N1206.

The amplifier output signal flows into Tee resistor R1206 from thecollector of Q1201 to node N1206. Output resistor R1207 couples theoutput of amplifier 1205 to load block at node N401.

The amplifier bias levels (V1201 and V1202) depend on the throughputpower level, load impedance (Z402), potential VSWR generated off theload, and injected noise levels. The levels are chosen to insure thatthe amplifier has sufficient voltage swing to accommodate the abovecharacteristics without railing against either bias supply. C1201 andC1202 are DC blocking capacitors used respectively to AC couple thereference and feedback signals into the amplifier. AC coupling in thismanner avoids disruption of the amplifier bias point at high frequency.In another embodiment, the output signal into R1206 is AC coupledthrough a series DC blocking capacitor.

The selection of R1202 depends on several factors. The value should belarge enough to achieve high gain in the amplifier. However, the valueneeds to be low enough so that the output impedance of the amplifier islow so that its characteristics continue to approximate a voltagesource.

Emitter Follower Embodiment

FIG. 13 is an embodiment in which the present invention is implementedwith a Class A amplifier and emitter follower. Electronic isolator 1300is coupled to source block at node N301. Isolator 1300 is coupled toload block at node N401. N-Type transistor Q1201 and resistors R1201,R1202, R1203 and R1204 comprise Class A amplifier 1305. Positive voltagebias V1201 couples amplifier 1205 to ground at node N1201. Negativevoltage bias V1202 couples amplifier 1205 to ground at node N1204.Resistors R1201 and R1202 are coupled to the positive voltage bias V1201at node N1201. Resistor R1201 is coupled to the base of transistor Q1201at node N1202. Resistor R1202 is coupled to the collector of transistorQ1201 at node N1203. Resistors R1203 and R1204 are coupled to negativebias V1202 at node N1204. Resistor R1203 is coupled to the base oftransistor Q1201 at node N1202. Resistor R1204 is coupled to the emitterof transistor Q1201 at Node N1205.

DC blocking capacitor C1201 is used to AC couple the reference signalinto amplifier 1205. Accordingly, C1201 couples source block at nodeN301 to the emitter of Transistor Q1201 at Node N1205. DC blockingcapacitor C1202 is used to AC couple the feedback signal into theamplifier. Accordingly, C1202 couples the base of transistor Q1201 atnode N1202 to node N1206. Isolator input resistor R1304 couples sourceblock at node N301 to capacitor C1202 at node N1206.

Emitter follower 1310 is comprised of resistors R1301, R1302, R303 andtransistor Q1301. Resistor R1301 couples the base of transistor Q1301 tothe collector of transistor Q1201. Resistor R1302 couples the base oftransistor Q1301 to ground. Resistor R1303 couples the emitter oftransistor Q1301 to ground. The collector of transistor Q1301 is coupledto amplifier 1305 at node N1201.

Tee resistor R1305 couples the emitter of transistor Q1301 to inputresistor R1304 and output resistor R1306 at node N1206. Output resistorR1306 couples the electronic isolator to load block at node N401.

An advantage of using an emitter follower embodiment is that R1202 canbe made large providing a high gain from the amplifier. Similarly,coupling the output from the emitter of the emitter follower provides alow impedance source for driving Tee resistor R1305.

Power Amplifier Distortion Reduction Embodiment

FIG. 14 illustrates an embodiment of the present invention in which thetopology of the isolator reduces signal distortion resulting fromoperation of the power amplifier. By moving the isolator sense inputfrom the output of a power amplifier to the input (or other undistortedrepresentation of the input) and adjusting the gain of the controlledsource appropriately, the power amplifier induced distortion is includedin the noise that is reduced by the isolator. Power amplifier A1401should be designed to provide relatively low distortion.

This embodiment also has the effect of including the time delay of thesignal through the power amplifier A1401 in the incident power path ofthe isolator. This provides a value against which to match the controlcircuitry delay.

As in the previous embodiments, V301 represents the signal source withits source resistance R301, and Z402 represents the input impedance ofthe next circuit. V401 represents the source of noise being injectedinto the system through its source impedance Z401. Electronic isolator1400 is coupled to source block at node N301. Isolator 1400 is coupledto load block at node N401.

Power amplifier A1401 is coupled to source block at node N301. ResistorR1401 represents the output resistance of amplifier A1401. ResistorsR1402 and R1403 constitute a resistive voltage divider that produces asample of the output signal from power amplifier A1401. Resistor R1402is coupled to resistor R1401 at node N1401 and to resistor R1403 at nodeN1402. Resistor R1403 couples R1402 to ground. Divider U1401 divides thesampled power amplifier output at node N1402 by the input voltage topower amplifier A1401 at node N301 to produce an output signal that isrepresentative of the voltage gain of power amplifier A1401. The outputof U1401 adjusts the resistance of variable resister R1411 based on thecalculated power amplifier voltage gain. In one embodiment, theadjustment of resistor R1411 is accomplished using digital controlcircuitry. In another embodiment, resistor R1411 is adjusted usinganalog control circuitry. R1411 is coupled to source block at node N301.

Resistors R1411, R1406 and R1407 together comprise a resistor dividernetwork used to set the isolator controlled source function gain.Resistor R1406 couples resistor R1411 to resistor R1407. Resistor R1407couples R1406 to ground. The positive terminal of operational amplifierA1402 is coupled to resistors R1406 and R1407 at node N1403. ResistorsR1408 and R1409 provide voltage gain for the amplifier stage. This isnecessary because the reference input signal to amplifier A1402 is beingtaken from the input of amplifier A1401 rather than the output. Thus,the reference signal is smaller than the feedback signal. Accordingly,the negative terminal of amplifier A1402 is coupled to resistors R1408and R1409 at node N1404. Resistor R1409 couples resistor R1408 toground. Resistor R1408 couples the divider network to resistor R1404 atnode N1405. Resistor R1404 couples the divider network to resistor R1401at node N1401.

The output current of amplifier A1402 flows through resistor R1410 tonode N1405. At node N1405, resistor R1405 couples the isolator circuitto load block at node N401.

RF Switch Embodiment

FIG. 15 illustrates an embodiment of a RF switch for use in one or moreembodiments of the present invention. In RF switch 1500, diodes D1501and D1502 are clamps limiting the reflected peak voltage seen by theisolator active circuitry. D1501 and D1502 are selected so as to providean easily detectable degree of rectification at the maximum operating orreflected power frequency the circuit will encounter. Positive voltageclamp supply V1501 is coupled to the cathode of D1501 and is ofsufficient magnitude so as to reverse bias D1501 under all normaloperating conditions. Negative voltage clamp supply V1502 is coupled tothe anode of D1502 and is of sufficient magnitude so as to reverse biasD1502 under all normal operating conditions. The negative terminal ofV1101 and positive terminal of V1502 ground the circuit at node N1504.

Current sense resistor R1501 couples the anode of D1501 to current senseresistor R1502 at node N1501. Resistor R1502 couples the cathode ofdiode D1502 to resistor R1501 at node N1501. Input to RF switch 1500 iscoupled to resistors R1101 and R1502 at node N1S01. The voltages acrossresistors R1501 and R1502 are inputs to control circuit 1505 and controlcircuit 1510, respectively. Control circuits 1505 and 1510 switch thebias voltages on RF switch diodes D1503 and D1504.

DC blocking capacitor C1501 couples RF switch input at node N1501 to theanode of diode D1504 at node N1502. DC blocking capacitor C1503 couplesthe cathode of D1504 to the output terminal of RF switch 1500. DCblocking capacitor C1502 couples RF switch input at node N1501 to theanode of diode D1503 at node N1503. Inductors L1501, L1502, L1503,L1504, L1505, and L1506 are RF chokes whose function is tosimultaneously block transmission of the RF signal through the inductorand provide a low resistance dc path for circuit bias and controlsignals. Inductor L1501 couples the cathode of D1503 to ground. ResistorR1504 is connected in parallel across inductor L1501.

Bias switches Q1501, Q1502, Q1503 and Q1504 can be any switching devicessuitable and appropriate for the application and known to those of skillin the art. In one embodiment, bias switches Q1501, Q1502, Q1503 andQ1504 are bipolar semiconductor devices. In another embodiment, the biasswitches are field effect transistors (FETs).

The bias current to RF switch 1500 is supplied by switch bias supplyV1503. From node N1504, bias supply V1503 couples to switch Q1502 atnode N1505. Switch Q1502 couples V1503 in series to resistor R1505.Inductor L1504 couples resistor R1505 to the anode of diode D1504 atnode N1502. Resistor R1506 is intended to function as a matched dummyload if the output of the RF switch is shorted to ground. Resistor R1506is coupled in parallel to diode D1504. Inductor L1506 couples thecathode of diode D1504 to ground. Inductor L1505 couples the anode ofdiode D1504 in series to switch Q1503. Switch Q1503 in turn couplesinductor L1505 to the anode of diode D1502.

From node N1505, switch Q1501 couples V1503 and Q1502 to series coupledresistor R1503 and inductor L1502. Inductor L1502 and inductor L1503 arecoupled to the anode of diode D1503 at node N1503. Switch Q1504 couplesthe anode of diode D1502 to inductor L1503.

Electronic Isolator Implemented with Crossover Networks

FIG. 16 illustrates an alternate embodiment of the Electronic Isolatorusing crossover networks. In the embodiments of the invention previouslydescribed, the only explicit frequency limitation has been the maximumoperating frequency achievable using operational amplifiers. Inpractice, there are few circuits that require continuous transmission ofall frequencies between DC and microwave frequencies. The typicalapplication requires the transmission of one or more bands offrequencies. FIG. 16 shows an embodiment of the present invention foruse in applications where the transmitted frequency band issignificantly above the maximum operating frequency of an operationalamplifier. In this topology, the output of the operational amplifier isconnected in series to the controlled voltage source such that bothcircuits drive the tee leg resistor. The controlled source providesin-band isolation in the manner of the embodiment described in relationto FIG. 6, but has an operating frequency range that does not overlapthat of the operational amplifier. Since there are no source signalswithin the operating frequency range of the operational amplifier, itattempts to provide complete isolation by removing any signal present inthis range. It functions as an active, low frequency noise cancellationfilter.

In the present embodiment, there is a band of frequencies between theoperating bands of the two series amplifiers in which the electronicisolator will provide no active noise cancellation. In manyapplications, this will not pose a problem for the system. However, insome applications, noise signals in the dead band may pose a significantproblem for the system. Solutions to this problem include the use ofactive or passive band reject filters, or the addition of anothercontrolled source in series in the tee leg, covering the problemfrequency band.

In the embodiment of the present invention shown in FIG. 16, electronicisolator 1600 is coupled to source block at node N301. Isolator 1600 iscoupled to load block at node N401. The isolator is connected to thesource block at node N301 by resistors R501 and R801. R801 is connectedto resistor R802 at node N801. Together, they form a resistor dividerfrom which node N801 provides the input to the operational amplifierA1601 and controlled source V1601. Resistor R1601 couples theoperational amplifier reference signal from node N801 to the plus inputof A1601 at node N1601. R1601 is also coupled to capacitor C1601 at nodeN1601. R1601 and C1601 form an R-C filter for the plus input of A1601.Capacitor C1601 provides an AC ground at the plus input of A1601 at thelowest output signal frequency from the source block. This filtering isnecessary in general because the operational amplifier, althoughincapable of processing the high frequency output signal from the sourceblock, may have its normal operation disturbed by the presence of thesesignals.

This embodiment is used where there are no source signals within theoperating frequency limits of operational amplifier A1601. Under theseconditions, there are alternate embodiments where the plus referencesignal of A1601 is obtained from node N301 or ground. In theseembodiments, resistor R1601 is connected to either node N301 or groundinstead of node N801. Resistor R1602 receives the output of A1601.Capacitor C1602 is coupled to R1602 at Node N1602. Similar to the ACground produced by capacitor C1601 on the plus input of A1601, capacitorC1602 provides an AC ground for the tee leg of the structure. Togetherwith resistor R1602, they isolate the output of the operationalamplifier A1601 from the high frequency signals present. Resistor R1602couples the output of operational amplifier A701 into the tee leg of theisolator at node N1602. The feedback signal to the negative input ofoperational amplifier A1601 is shown taken from node N1602 rather thandirectly from the operational amplifier output as in the embodimentdescribed for FIG. 8B. This is to avoid the potential large reduction inisolation due to the high total series resistance of resistors R1602,R1603, and R502. In an alternate embodiment in which this condition isacceptable, the feedback signal to the negative input of operationalamplifier A1601 is connected directly to its output. In otherembodiments, the negative feedback is taken from nodes N501 or N1603. Inthese embodiments, an R-C filter is added to the negative input ofoperational amplifier A1601 to isolate it from the high frequencysignals present in the same manner as R1601 and C1601 isolate the plusinput of A1601.

V1601 is a controlled voltage source with source resistance R1603. Ittakes its input from node N1602 and is coupled in series to resistorsR1603 and R502. The voltage controller is coupled to ground at itsnegative terminal and to node N801 at its positive terminal. ResistorR502 is coupled to R501 and R503 at node N501. R503 couples the isolatorto load block at node N401.

Together with R1603 and R502, V1601 produces the asymmetric isolationeffect for in-band signals as described in the discussion of theembodiment illustrated in FIG. 6. In an alternate embodiment, controlledsource V1601 takes its input directly from node N301 if it has means ofadjusting its gain relative to node N301 other than resistive dividerR801 and R802.

In an alternate embodiment, the controlled source V1603 and operationalamplifier A1601 drive separate, parallel tee legs with separateresistors replacing R502, since the two amplifiers do not overlap intheir operating frequency bands. In other embodiments, multiple paralleltee legs can be added for additional source signal operating bands.

The various single-stage embodiments illustrated and described in FIGS.6, 7, 8A and 8B had multi-stage embodiments illustrated in FIGS. 9, 10and 11. Similarly, there are alternate embodiments for the embodimentshown in FIG. 16 and the additional embodiments described in thediscussion of FIG. 16.

Electronic Isolator with Augmented Out-of-Band Isolation

Many electronic circuit applications have signals that are constrainedto specific frequency limits. In one or more embodiments of the presentinvention, the use of reactive components in the circuit substantiallyenhances performance in applications in which source signals are singlefrequency or have very narrow bandwidth.

FIG. 17 illustrates an embodiment of the present invention in whichreactive components are incorporated into the circuit. The embodiment issimilar to that illustrated in FIG. 8B with the following exception:resistor RS03 of FIG. 8B has been replaced by inductor L1701, capacitorC1701 and resistor R503 connected in series. This three component seriesnetwork is coupled to node N501 and to the load block at node N301. Thevalues of L1701 and C1701 are chosen such that their series resonantfrequency is the mid-band of the source signal. Thus configured, thisnetwork contributes a negligible amount to the insertion loss of theisolator. The increased out-of-band impedance of the output leg producedby the tuned circuit substantially increases the attenuation ofout-of-band signals entering the isolator at its output connection tothe load block.

In one embodiment, the L-C or R-L-C networks of FIG. 17 are replaced bymultiple L-C and/or R-L-C networks connected in parallel, and staggertuned to allow transmission of wider bandwidth input signals. In anotherembodiment, parallel L-C or R-L-C networks are incorporated into thepresent invention to block or provide substantially increased isolationat specific frequency bands. In practice, the number and location ofreactive components incorporated into any Electronic Isolator embodimentcan vary widely and are highly dependent on the application and thenature of the signals being transmitted through the isolator. Reactivenetworks can be placed in any or all of the legs of the isolatorcircuit, regardless of its configuration.

The embodiments of the invention described above collectively use a teeattenuator configuration and single conductor inputs and outputs. As iswell known to those of skill in the art, equivalent embodiments can beeasily structured around other attenuator forms. A two-stage version isthe equivalent of using pi attenuator where some resistors functionsimultaneously as stage input and output resistors. A bridged teestructure can also be used as the base configuration. This is not apreferred topology since the bridge resistor will effectively shunt theisolator in the absence of a second, floating operational amplifier orcontrolled voltage source to control current through this path.

Similarly, many systems use multiple-conductor inputs and outputs suchas twisted pair and twisted shielded pair lines, three-phase or a moregeneral multi-conductor, multi-phase system. For twin conductor systems,the Electronic Isolator can be configured around a classic latticeattenuator topology. It can also be implemented using 2 tee topologiesto provide independent isolation for each conductor. This is also thepreferred embodiment for 3-phase and multi-phase systems. In principle athree-phase delta configuration can be implemented, but this embodimentwill require multiple floating bias power supplies and sources that arenot typically desirable.

Thus, an electronic circuit isolator has been described.

1. An electronic isolator between a source stage and a load stage,including configuring means for configuring said isolator to appear asan infinite impedance to said source stage.
 2. (canceled)
 3. (canceled)4. (canceled)
 5. The electronic isolator of claim 1 wherein saidconfiguring means is an operational amplifier with negative feedback. 6.The electronic isolator of claim 5 wherein said configuring meanscomprises a gain controlled stage.
 7. The electronic isolator of claim 6wherein said gain controlled stage is a divider network.
 8. Theelectronic isolator of claim 3 further including an input amplificationcircuit between an electrical input of said source stage and anattenuation circuit network.
 9. The electronic isolator of claim 8including means for configuring control signals for said controllablesources.
 10. The electronic isolator of claim 9 wherein said controlsignals include reference signals and negative feedback signals.
 11. Theelectronic isolator of claim 10 wherein said configuring means includescircuitry for determining the gain of an input amplification circuit.12. The electronic isolator of claim 10 wherein said input amplificationcircuit gain controls said reference signal level.
 13. An electronicisolator between a source stage and a load stage comprising: anelectrical input comprising at least one source electrical connectionconnected to the source stage, an electrical output comprising at leastone load electrical connection to the load stage, at least one circuitpath into which electrical noise is directed away from the source andload electrical connections.
 14. (canceled)
 15. The isolator of claim 3wherein said isolator redirects noise present on the electrical outputto a circuit path other than the electrical connections to the sourcestage.
 16. (canceled)
 17. The electronic isolator of claim 13 wherein atleast one of said electrical input and said electrical output comprise aplurality of conductors not using ground signal return paths.
 18. Theelectronic isolator of claim 15 wherein at least one of said electricalinput and said electrical output comprises at least one conductor pairconducting differential signals.
 19. The electronic isolator of claim 18further including an attenuation circuit network comprising at least onelattice attenuator network for each conductor pair.
 20. The electronicisolator of claim 17 wherein at least one of said electrical input andsaid electrical output comprise groups of three conductors eachconducting three phase delta configuration signals.
 21. (canceled) 22.The electronic isolator of claim 13 wherein said controllable source isan operational amplifier.
 23. The electronic isolator of claim 13wherein said controllable source is an amplifier circuit.
 24. Theelectronic isolator of claim 19 wherein said amplifier circuit includesa Class A amplifier.
 25. The electronic isolator of claim 24 whereinsaid amplifier circuit includes an emitter follower output stage. 26.The electronic isolator of claim 25 wherein said amplifier circuitincludes a Class A amplifier.
 27. The electronic isolator of claim 13wherein at least one of the input and the output of said controllablesources comprise circuit structures providing the function of series,direct current blocking capacitors.
 28. The electronic isolator of claim13 wherein said attenuation circuit networks comprise circuitryproviding the function of a networks of resistors.
 29. The electronicisolator of claim 13 wherein said attenuation circuit networks includeat least one active circuit that determines the impedance of at leastone circuit path within at least one of said attenuation circuitnetworks.
 30. The electronic isolator of claim 13 wherein at least oneof said attenuation circuit networks contains circuits providing thefunction of frequency responsive passive components.
 31. The electronicisolator of claim 13 wherein the frequencies of said noise redirected tosaid circuit paths other than the electrical connections to the sourcestage are limited by the operating frequency range of said controllablesources.
 32. The electronic isolator of claim 31 wherein a plurality ofsaid controllable sources are responsive to distinct, non-overlappingfrequency bands.
 33. The electronic isolator of claim 32 wherein atleast one of said controllable sources is an operational amplifier. 34.The electronic isolator of claim 32 wherein said controllable sourcesare corrected in series driving one of said electrical noise redirectioncircuit path.
 35. The electronic isolator of claim 32 wherein saidcontrollable sources drive separate noise redirection circuit pathswherein said noise redirection circuit paths are connected to a commonnode.
 36. The electronic isolator of claim 13 wherein said attenuationcircuit networks include at least one T-configuration network.
 37. Theelectronic isolator of claim 13 wherein said attenuation circuitnetworks include at least one Pi-configuration network.
 38. Theelectronic isolator of claim 13 wherein said attenuation circuitnetworks include at least one Bridged-T-configuration network.
 39. Theelectronic isolator of claim 13 wherein said attenuation circuitnetworks include at least one lattice configuration network.
 40. Theelectronic isolator of claim 13 wherein said attenuation circuitnetworks include said circuit paths into which said electrical noise isredirected.
 41. The electronic isolator of claim 13 including means forconfiguring the control signals for said controllable sources.
 42. Theelectronic isolator of claim 41 wherein said configuring means include areference signal.
 43. The electronic isolator of claim 42 wherein saidreference signal is adjusted to compensate for signal loss occurring inpart of said attenuation circuit networks.
 44. The electronic isolatorof claim 43 wherein said reference signal adjustment is made using atleast one resistor divider network.
 45. The electronic isolator of claim44 wherein said resistor divider networks are connected to saidelectrical input.
 46. The electronic isolator of claim 43 wherein saidreference signal adjustment is made using an active circuit which tracksand scales said electronic isolator input signals.
 47. The electronicisolator of claim 41 wherein said configuring means includes at leastone negative feedback signal.
 48. The electronic isolator of claim 47wherein said negative feedback signal originates at a circuit node intowhich said electrical noise is redirected away from said electricalinput.
 49. The electronic isolator of claim 48 wherein at least one ofsaid controllable sources is an operational amplifier connected as avoltage follower.
 50. The electronic isolator of claim 13 furtherincluding an input amplification circuit between said electrical inputand said attenuation circuit networks.
 51. The electronic isolator ofclaim 50 including means for configuring control signals for saidcontrollable sources.
 52. The electronic isolator of claim 51 whereinsaid control signals include reference signals and negative feedbacksignals.
 53. The electronic isolator of claim 52 wherein saidconfiguring means includes circuitry for determining the gain of saidinput amplification circuit.
 54. The electronic isolator of claim 52wherein said input amplification circuit gain controls said referencesignal level.
 55. The electronic isolator of claim 52 including meansfor reducing said negative feedback signals.
 56. The electronic isolatorof claim 13 wherein said controllable sources redirect noise appearingon the electrical input away from the electrical output and into saidnoise redirection circuit paths.
 57. (canceled)
 58. The electronicisolator of claim 13 including means for detecting conditions ofanomalous operation.
 59. The electronic isolator of claim 58 includingmeans for producing at least one control signal to said source stage todetermine the electrical power entering said electronic isolatorelectrical input.
 60. The electronic isolator of claim 59 includingmeans for producing a time delay between the time of detection of onesaid conditions of anomalous operation and the production of saidcontrol signals.
 61. The electronic isolator of claim 59 whereincontrollable source is configured so as to absorb the maximum, peak,source stage generated, electrical signal power present under saidconditions of anomalous operation during the time between the time ofdetection of one of said conditions of anomalous operation and saiddetermination of said electronic isolator electrical input.
 62. Theelectronic isolator of claim 58 including means for switching saidelectronic isolator electrical output away from said load stage.
 63. Theelectronic isolator of claim 62 including means for dissipating theelectrical input power to said electronic isolator in at least one dummyload resistor.
 64. The electronic isolator of claim 63 wherein said atleast one dummy resistor is internal to said electronic isolator. 65.The electronic isolator of claim 62 wherein said switching means is acircuit including at least one relay.
 66. The electronic isolator ofclaim 62 wherein said switching means is a circuit including at leastone bipolar transistor.
 67. The electronic isolator of claim 62 whereinsaid switching means is a circuit including at least one field effecttransistor.
 68. The electronic isolator of claim 62 wherein saidswitching means is a diode, RF switching circuit.